Electrochromism is a special phenomenon displayed by some materials of reversibly changing color between a colored state at low transmittance and a bleached state at high transmittance when the materials undergo a redox reaction by injecting or extracting charge under a reversible high-low or positive-negative external electric field. Such phenomenon shows a reversible change of color and transparency in appearance, and has broad application prospect in the fields of electrochromic windows, electrochromic displays and the like. Electrochromic materials can be classified into inorganic electrochromic materials and organic electrochromic materials. A typical representative of the inorganic electrochromic materials is tungsten trioxide (WO3). At present, the electrochromic device using WO3 as functional material has been industrialized. Organic electrochromic materials mainly include polythiophenes and derivatives thereof, viologens, tetrathiafulvalene, metal phthalocyanines compounds and the like. The electrochromic device using the viologens as functional material has been put into practical use. Compared with the inorganic electrochromic materials represented by the transition metal oxide, organic electrochromic materials, such as polyaniline, polypyrrole, polythiophene, viologen and the like, have the advantages of having rich colors and easy molecular design, and thus are preferred by researchers.
The insolubility of the polythiophenes due to its rigid main chain presents difficulties in producing an electrochromic device from such electrochromic polymeric materials. Typically, the polymer is deposited directly onto the electrode surface to form a polymer film by electrochemical polymerization methods. However, the existed electrochemical polymerization method is not competent in forming electrochromic device having a large area. Accordingly, the present invention is particularly provided in view of this.